Henry S. Belson

Elastic Constants, Thermal Expansion, and Debye Temperature of Lead Telluride

Measurements of the elastic constants and thermal expansion of PbTe have been made from 4.2° to 303.2°K. The extrapolated 0°K values for C44, (C11−C12)/2, and (C11+2C12)/3, respectively, are 1.514±0.009, 6.184±0.066, and 4.560±0.042×1011 dyn/cm2. At 303.2°K these values are 1.344±0.008, 5.016±0.057, and 4.107±0.037×1011 dyn/cm2. Intermediate values are presented graphically, as are the thermal‐expansion data. The linear coefficient of thermal expansion is found to be 20.4±0.4×10−6/°C at room temperature. The 0°K Debye temperature is calculated to be 176.7°±0.5°K.

Elastic properties of rare‐earth‐iron compounds

Ultrasonic velocities have been measured and used to determine the elastic moduli of the highly magnetostrictive compounds: TbFe2, TbFe3, and ErFe2. A huge ΔE effect of 90% has been calculated for TbFe2 from our static stress‐strain data.

Shiftless Fermi Level in Iron, Nickel, and Cobalt

Walmsley has suggested a method whereby one can deduce the relative density of states at the Fermi level for spin‐up and spin‐down electrons. This method compares the shift in Fermi level with applied magnetic field for a magnetic metal with that of a nonmagnetic metal by measuring the voltage induced across the plates of a capacitor, one plate of which is of each metal. His measurements indicate that all Fermi surface electrons have moments parallel to the bulk magnetization. We have repeated and extended these measurements and get different results. We have measured the voltage induced in Fe‐Al, Ni‐Al, and Co‐Al capacitors (evaporated magnetic metal on one side of a high‐permittivity ceramic wafer and Al on the other) as a function of applied field. We have also measured a series of Fe‐Cu capacitors of different thicknesses of iron, and a capacitor constructed of rolled iron foil and aluminized Mylar. Voltages appear which relate to the change of magnetization rather than to applied field. A magnetostri...

High‐Temperature Magnetostriction in Alloys

Conventional theory predicts that the magnetostriction coefficients h1 and h2 fall monotonically to zero with increasing temperature. Callen and Callen have proposed a theory to account for the presence of an anomalous peak in h1 for iron just below the Curie temperature, based on the fact that an ellipticity in the magnon spectrum permits a lowering of the free energy by crystal distortion. An anisotropic magnon‐phonon interaction near the Brillouin‐zone boundary is largest when thermal magnon renormalization has lowered the magnon spectrum to degeneracy with the phonon spectrum, at which a peak in h1 occurs. Thus, iron whose Curie temperature is substantially greater than the Debye temperature shows this effect. To test this theory further we have measured h1 in a cubic single crystal of 56.96 wt% Ni‐42.82 wt% Co with Curie and Debye temperatures approximately those of iron, using a capacitative method. We find a monotonic decrease in h1 from 1.49 × 10−4 at 80°K to close to zero at 1000°K, and no hint o...

Anisotropic Magnetization of Ytterbium Orthoferrite

The magnetization of single‐crystal ytterbium orthoferrite (YbFeO3) was measured from 4.2° to 300°K in fields1 up to 110 kOe. At high temperatures a small spontaneous moment appears along the c direction. The magnetization is proportional to field along the a, b, and c directions. As the temperature is lowered, the field‐dependent magnetization parallel to a increases rapidly and approaches a saturation value of 3.2 μb at 4.5°K. Along the c direction, an anomalously small increase in spontaneous magnetization with decreasing temperature is observed below 100°K. In addition, below 2.3°K the magnetization becomes temperature independent but still retains a large field dependence. From this we predict that either: (1) the magnetic unit cell is larger than the crystallographic cell, yielding Yb magnetic sublattices canted from the c direction; or (2) the Yb3+ ground state is not a Kramers doublet widely separated from the remaining levels. The high‐field magnetization along the b directions is markedly smalle...